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:.$                             242                              Connecting Rod.

shewn.     Trammel  between the  shoulders,  and square up the

vertical lines, as well as the end lines; measured from  these.

Next lay the rod flat as at c, and scribe the centre line round in a

similar manner to the last.    Punch centres, and place in lathe,

testing with chalk, and square-centreing.    Now set the poppet

head over by half the diameter difference, and turn the taper

portion up to the shoulder radii, as shewn at j, Fig. 240.    Set

\                                  the poppet head true again, and surface the ends of the rod, also

J\a                                  the shoulders up to the radii.    These last require very careful

turning.    They are to be roughed out by means of a combination

of surfacing and  traverse  feed, and   semi-finished  by a broad

tool  ground  to the  curve,  the  position of which is gradually

changed by turning round the top rest until the whole curve is

gone over piece by piece.    The last finish is given by hand with

the same tool very sharply ground.    Of course the work must be

continually tried by means of a sheet iron copy called a ' tern-

,                                    plate/ shewn at r> and E, the lathe being stopped at each trial;

n"                                  and the outer curve of the solid end is to be finished in like

jj     ,                       manner.

<j     j                            Remove from the lathe, finished, but not polished, and lay on

f                            the surface plate as at F, packing till level.    Scribe the thickness

of the butt and solid end, then fasten, as at G, across a shaping

^                       machine having two tables, and shape.    Similarly also for the

depth.   Return to  the marking table.    Scribe the centre line

;                       afresh, and plot out the square hole in solid end as at j; do this

on both sides, and well dot all round it.    This may now be cut

out in one of two waysó(i) a hole may be drilled large enough

i                        o pass a slotting tool, by twist drill and pin drill, and the rest of

j                       the work "done by slotting; (2) a probably better method, is to

J                       take out all round by means of slot-drilling tool, drilling, say, a

;                       quarter of an inch down, traversing all round as at K, then a little

i                       further down, and so on till the hole is completely cut, finishing

J                       the sides with a milling cutter and the corners with a corner tool

;                       There is then very little work left for the file.

Now mark off the bolt-holes at L, on both sides of the solid
end, together with the oil-hole, and the cotter-hole at M. Drill
the bolt-hole from each side, broach through, and countersink
the oil-hole. Take out the cotter-hole in slot-drilling machine